1. Field of the Invention
The present invention relates generally to the field of orthodontics. More specifically, the present invention discloses a system for producing orthodontic aligners by CNC machining.
2. Statement of the Problem
The infiltration into dentistry of new computer-based processes involving 3D imaging of human teeth began in the early 1990's. Particularly in orthodontics, these new digital technologies are providing orthodontists with fundamentally new tools for delivering orthodontic treatment. Early patents in this field such as U.S. Pat. No. 5,139,419 to Andreiko et. al. described the early methods for the 3D imaging of teeth. The subsequent manipulation of virtual occlusion to obtain information necessary for orthodontically correcting tooth position according to a virtually-determined ideal has been a key step in advancing the standard of care within orthodontics. In recent years laboratory processes related to the 3D imaging of a patient's dentition have continued to expand and have served as the basis for the provision of a number of new commercial services that have become available to orthodontists.
An example of the successful orthodontic application of these digital technologies is seen in the commercial service known as the Invisalign program. The Invisalign program is based on U.S. Pat. No. 5,975,893 (Chishti et al.), and many related patents including in particular U.S. Pat. No. 6,398,548. The Invisalign program is described in full detail below because it illustrates all of the technical aspects of digital applications within orthodontics. It illustrates the business aspects of new digital services, and it depicts the advantages of new types of technology being introduced into the practice of orthodontics. The current invention accommodates or impacts many of these areas. To follow then is an exhaustive description of the Invisalign program to best contrast the description of the improvements and advantages provided by the present invention that follows.
The Invisalign program involves the creation of a patient's virtually treated finished occlusion. This is the finished or ideal occlusion produced strictly within the confines of computer software that can be displayed on a computer monitor. From that, output methodologies are used to fabricate a series of progressive polymeric tooth positioners. Invisalign positioners, called aligners, are generally similar in appearance to appliances known as mouth guards worn by sports participants or the soft plastic appliances worn at night to protect teeth against the destructive effects of bruxism. The Invisalign program is marketed to the general public as an improved alternative to conventional orthodontic braces and is referred to in TV advertising as “invisible braces.”
Invisalign tooth positioners are thin, transparent U-shaped plastic appliances formed over computer-generated physical forming patterns grown from the virtual model of the virtual teeth described above. The process for forming aligners uses a combination of vacuum, pressure and heat. This forming process is informally referred to within the orthodontic laboratory community as the “suck down” process and as such, aligners are informally considered to be suck-down-type appliances.
The Invisalign-type tooth aligners are formed from a thinner material than the traditional mouth guard-type appliance. One commonly used material known as polycarbonate (PC) is a harder but still relatively flexible and somewhat elastic polymeric material. Other materials such as co-polymers including ethylene vinyl acetate and polypropylene as well as polypropylene alone, and other olefin-type plastics are also used for sucking-down aligners. In the vast majority of cases, the raw material is in sheet form. In other words, aligners are formed from small sections of standard industrial polymeric sheet materials. The materials used are mostly sourced industrially, and they are not necessarily produced specifically for orthodontic aligner application. The commodity-type sheet material is typically manufactured using a continuous extrusion process or a casting process. Sizing of the sheets typically used for suck-down-type appliances can be many feet wide by many feet long, and can range in thicknesses from 0.75 mm (0.030 in.) up to 2 mm (0.079 in.) but thinner and thicker materials are used in special cases.
In order to produce a series of Invisalign-type tooth aligners, an Invisalign technician first scans a patient's upper and lower model set as a means to obtain CAD-manipulatable virtual models of a patient's teeth, gums and soft tissue. A model set normally consists of one upper and one lower plaster model of the teeth, palate and gums. Like Andreiko's methods, such a digital model, once obtained in this manner can be displayed and altered using a software tool known as a computer-aided design (CAD) program. Once the virtual model of the original malocclusion has been obtained, an Invisalign technician will then undertake steps involving extensive manipulation of the virtual malocclusion. This involves extensive repositioning of the teeth according to a comprehensive and sequential procedure, ultimately arriving at a finished or ideal occlusion for that patient. The finished occlusion, even though virtual, is nonetheless consistent with the complete repositioning of the patient's upper and lower occlusion that would result at the end of fully successful conventional orthodontic treatment.
As can be appreciated, after the steps described above are accomplished, an Invisalign technician then possesses two versions of the patient's teeth available within the virtual CAD environment. One version represents the original malocclusion and the other represents the ideal occlusion. In other words, the technician has the beginning and the end states.
It must be noted that the Invisalign technician is not a trained orthodontist. Since the 3D imaging and the corrected case are virtual, they can easily be made available to the patient's doctor online through the internet. Using a special viewing and metrix tool package provided to the doctor online over the internet, the doctor can examine the correctness and precision of the steps taken by the Invisalign technician in full detail. The doctor can approve the work performed by the technician, or provide additional instructions to insure that the actions of the technician are consistent with the doctor's treatment plan for the patient. Ultimately, the doctor must provide his formal approval for the process to continue.
After the attending doctor approves the technician's work-up, the next step in the Invisalign process involves the creation of typically 15 to 25 incremental progressive physical forming models. Each of these forming models represents a snapshot of the patient's future occlusion at specific incremental steps along his or her proposed treatment sequence falling between the beginning and the end conditions as described above. To accomplish this, the Invisalign technician creates a virtual “first transition model” that sees a slight repositioning of all or most of the teeth. This first transition model sees some or all of the teeth being subtly moved from their original pre-treatment positions to a virtual first transition position that is in the direction of their intended finished positions. Similarly, a second virtual transition model is created that sees the virtual teeth being moved again slightly further in the desired directions. The objective of the Invisalign technician is to create a series of progressive models, each biased slightly further than the previous one, and each moving the teeth slightly closer to their finished target positions. A final forming model will take the teeth from the series of transition positions and move them into their final, desired positions.
Once such a series of virtual intermediate forming models has been created and a final forming model has been created by the Invisalign technician, the digital code representing each of the models in the series is directed to operate a digital, computer numerically-controlled (CNC) machine known as a rapid prototyping machine. Within a rapid prototyping machine, the series of physical forming models are grown using one of a group of known processes, such as stereo lithography or 3D printing. The growing step results in the production of hard, physical duplicates of each of the series of virtual intermediate models and the final model. These are not virtual models but rather hard, physical models that can be held by hand.
The next step of the Invisalign process sees each of the series of physical models being in turn mounted in a suck-down machine where a combination of pressure, heat and vacuum is used to form the actual series of progressive aligners from plastic sheet material of a constant thickness. Once the series of progressive aligners are formed and trimmed, they are sequentially labeled, packaged and shipped to the attending orthodontist. The orthodontist then schedules an appointment for the patient, at which time the aligners and instructions for their use are given to the patient. The patient will be instructed to begin wearing the first set of aligners for a period of time, typically two weeks. After that, the first set is discarded and the patient transitions to the next set of the series and so on.
The aligners serve to urge the patient's teeth to move according to the positional biases created virtually be the Invisalign technician. The teeth are progressively biased and urged to move in desired directions toward their predetermined finished positions by the resilience of the polymeric material of the aligner. In response to the gentle but continuous forces delivered by the aligners, certain physiological processes involving the creation and resorbtion of the bone supporting the roots of the teeth are initiated. The net result is the slow, progressive orthodontic movement of the roots of the teeth through the underlying bone toward desirable positions and orientations.
The orthodontists role in aligner-based treatment is essentially relegated to that of monitoring the physiological response of the teeth and monitoring the patient's cooperation with the treatment schedule. The attending orthodontist is not required to establish the progressive sequence or otherwise direct the treatment because the functionality of the aligners and the tooth-moving protocol is determined off-site by the Invisalign technician at the orthodontic service center. The orthodontist still must evaluate and approve the work-up provided by the Invisalign program.
As a whole, digital advancements in orthodontics have increased the versatility of the virtual occlusion data and have expedited or eliminated some traditional operatory steps. These trends can involve the introduction of new equipment and software into the orthodontic practice that has not been considered as standard dental laboratory equipment in the past. For example, doctors must acquire and become familiar with 3D analytical software, which is included with the Invisalign program in order to view the virtual occlusion created by an Invisalign technician as described earlier. Another example is CAT scanning equipment optimized for use in dental operatories, which is becoming commercially available for in-office installation. Similarly, acquisition of in-office scanning equipment and rapid prototyping equipment would move some of the Invisalign process steps from the commercial service center directly to the “back room” laboratory of an orthodontic practice. These are all aspects of what some refer to as the emerging “digital orthodontics.”
However, the large capital expenditures and technical sophistication required for existing digital orthodontic systems, such as the Invisalign program, have required the use of a central facility to produce aligners. This tends to increase costs and introduces an element of delay in meeting the needs of patients.
The conventional suck-down techniques of the type produced through the Invisalign program also limit the types of aligners that can be formed. Ideally, a thin sheet of polymeric material is used to form an aligner having an approximately constant wall thickness. In fact, vacu-forming often results in regions in the aligner having reduced or uneven wall thicknesses, which can be undesirable. Also, it is sometimes desirable to selectively create a thicker aligner wall adjacent to specific teeth (e.g., molars or an especially mal-positioned tooth) to exert greater corrective forces. This is very difficult or impossible to accomplish with conventional suck-down forming techniques.